(1) Field of the Invention
The present invention relates to a spectroscopic device for analyzing a sample by spectroscopy. This invention also relates to a method for detecting, by spectroscopy, an inhomogeneity in a sample as well as a method for determining, also by spectroscopy, the absorption and/or diffusion coefficient of such a sample, in particular implementing such a probe.
This invention is related to the field of the manufacture of the devices allowing carrying out an analysis of a sample by spectroscopy.
In this respect, it should be noted that spectroscopy is a technique largely implemented in industry and research when both solid and liquid samples should be analyzed.
(2) Description of the Prior Art
In fact, various types of spectroscopy are known, each of these types corresponding substantially to a range of wavelengths of the light emitted (UV, visible, infrared, near infrared, mid infrared, Raman), and allowing to characterize in particular some of these samples and/or to determine some characteristics of such a sample.
In particular, it is known to implement a spectroscopy technique for characterizing products formed, by way of non-restrictive examples, by pharmaceutical tablets, gels, emulsions, powders, flours, products in suspension.
More specifically, such a spectroscopy technique can then be implemented to determine the homogeneity and/or the uniformity of such a product.
In this respect, various methods allowing determining such homogeneity and/or such uniformity are known.
In particular, a first method consists in illuminating a sample at an illuminating point, and in measuring several series of spectra at a measuring point different from the illuminating point and fixed with respect to it.
In fact, this method consists, between two series of spectra, either in repositioning (manually or automatically) the sample in order to acquire spectra in different areas of this sample, or in mechanically stirring this sample (in particular using a mixer).
A first drawback of this method resides in that repositioning the sample takes a certain time. A second drawback of this method resides in that a bad repositioning of the sample induces a variation in the spectrum, which will be interpreted as an inhomogeneity, whereas it is, instead, a mere manipulation and/or positioning error.
In order to cope with these drawbacks, a new technique has been devised, which consists in submitting the sample to two measurements, one of which is in reflection, while the other one is in transmission. This technique however brings a new drawback consisting in that the spectra obtained are by no means comparable, since they correspond to lights having travelled over different distances with respect to the sample.
A second method, aiming at determining the homogeneity and/or uniformity of a product, consists in using a hyperspectral camera for acquiring a two-dimensional image of this product and comprised of a plurality of pixels.
In fact, this method consists, first, in acquiring at least one spectrum for each pixel of the image of the product and, afterwards, in analyzing and comparing to each other the spectrum or the spectra of these pixels.
This method advantageously allows analyzing the whole surface of the product and comparing spectra acquired in similar conditions (illumination of the sample, travel distances of the light with respect to this sample . . . ).
This method has a number of drawbacks. Thus, a first drawback of this method consists in that the time for acquiring the spectra is particularly long (namely in the range of several minutes), which makes it difficult to contemplate this method for continuously characterizing a product.
However, the main drawback of this method consists in that only the surface of the sample can be analyzed. Thus, this method allows by no means detecting the presence of a physical (agglomerate) or chemical (concentration of active substance) inhomogeneity located under the surface if the product and in depth in the product.